can1357/haruspex

Haruspex is a project that uncovers hidden or undocumented instructions in Intel computer processors. Modern CPUs have a massive list of commands they can understand, but not all of these commands are publicly documented. This tool acts like a digital detective, figuring out what those secret commands are and how they affect the processor's internal workings. It works by taking advantage of "speculative execution," a trick modern processors use to guess what work they will need to do next in order to run faster. Haruspex tricks the processor into trying out unknown commands through this guessing process. Even though the processor ultimately cancels the guessed work before it officially finishes, it leaves behind subtle clues in the chip's internal performance counters. By reading those clues, the project can deduce what the mystery command actually did. This tool is primarily for security researchers, low-level systems developers, and hardware enthusiasts. For example, a security researcher might use it to find an undocumented instruction that malware could exploit, or a developer writing highly optimized software might want to understand exactly how different commands flow through the processor's pipeline to make their code run as fast as possible. The project includes a component that runs inside the computer's core system to generate this data, and a web server that lets users browse the findings in an interactive table. The creator notes that the core code is essentially "pseudo-code" because some of the private tools used to build it cannot be shared, but it is written clearly enough for another developer to adapt for their own system.